1. Field of the Invention
The present invention relates to a receiving apparatus suitable for one that receives a digital broadcast signal subjected to interleaving.
2. Description of the Related Art
In recent years, the digital broadcast that performs transmission and reception in a digital system has been started. In the digital broadcast in Japan, an ISDB-T system is employed. In the ISDB-T system, a TS (transport stream) defined in the MPEG (Moving Picture Expert Group)-2 standard is subjected to signal processing such as error correction coding, interleave coding, digital modulation, and the like. Further, the TS is OFDM (Orthogonal Frequency Division Multiplexing) modulated and the modulated result is outputted.
Moreover, in the terrestrial digital broadcast, interleaving over relatively long time periods is employed. Noise is dispersed by interleaving to facilitate error correction, thus making it easy to achieve a decodable state even if a poor reception state occurs due to amplitude fluctuation by fading.
A large capacity is required for a memory for interleaving used in the terrestrial digital broadcast in which the number of pixels is large. To this end, Japanese Patent Laid-Open No. 2005-286504 (hereinafter referred to as Patent Document 1) discloses the technique for reducing a capacity of the memory for interleaving. In the proposal in Patent Document 1, in order to reduce the capacity of the memory for interleaving, information is compressed by pre-demapping before deinterleaving so as to reduce the number of bits.
However, there is need to specify a modulation scheme in order to perform pre-demapping. The modulation scheme can be grasped from transmission data after deinterleaving. However, in the case where a plurality of hierarchies is spread by interleaving as in the transmission system in Japan, a circuit for determining a modulation scheme must be prepared separately in order to specify the modulation scheme before deinterleaving.
Moreover, reliability information of transmission data is generally used in error correction processing. A general error correction code has correlation in time between signals. By use of reliability of information, weighting of error correction due to an error correction code with low reliability is reduced, allowing improvement in error correction accuracy.
However, in the technique disclosed in Patent Document 1, the reliability information calculated from a transfer function or the like and soft-decision information are combined to execute bit reduction due to pre-demapping. This makes it impossible to separate the reliability information and the soft-decision information from each other after interleaving, with the result that the reliability information cannot be used in error correction processing.